1. Field of the Invention
The present invention relates to a semiconductor memory device, and more specifically, to a composite memory device comprising an asynchronous memory device configured to operate at high speed, a synchronous memory device configured to operate in a page mode, and a synchronous memory device configured to operate in a burst mode all therein.
2. Description of the Related Art
A high performance system requires various kinds of memory devices each having excellent characteristics in one of performances such as speed and capacity. For example, the high performance system needs a cache memory to exchange data with a CPU at high speed, a nonvolatile memory to store a program, and a synchronous memory with a high-speed burst function to process high-capacity data at high speed. In a conventional system, however, these memories are embodied in separate chips.
FIG. 1 is a block diagram illustrating a conventional memory device.
The conventional system includes an asynchronous SRAM (Static Random Access Memory) 1 for high-speed data processing, a flash memory device 2 as a nonvolatile memory device, and a SDRAM (Synchronous Dynamic Random Access Memory) 3 configured to operate in a burst mode for high-capacity data processing at high speed. These memory devices 1, 2 and 3 share a system bus 4, and they are controlled by the same memory controller 5.
In the conventional system comprising a plurality of memory devices for each performing separate function, a memory controller controls memory devices individually. Therefore, the operation speed decreases because the data transfer operation is controlled at the system level even when data are exchanged among the memory devices, thereby degrading the operation efficiency of the whole system.